Add rodney viewport command for viewport and mobile emulation

[johnwards]

Summary

• Adds a new rodney viewport <width> <height> [--scale N] [--mobile] command that sets the browser viewport size via Chrome's EmulationSetDeviceMetricsOverride CDP call
• Adds rodney viewport --reset to clear the override and restore browser defaults (EmulationClearDeviceMetricsOverride)
• Adds --viewport WxH, --mobile, and --scale N flags to rodney start for configuring viewport at launch time
• Viewport settings are persisted in state.json and re-applied on each subsequent command, consistent with rodney's ephemeral-process architecture
• rodney screenshot now respects the active viewport by default instead of always overriding to 1280x720 — pass -w/-h to explicitly override

Bug fix

Also fixes a pre-existing bug where rodney start --show would hit the default: fatal("unknown flag: ...") case in the flag-parsing loop before the --show flag was checked in a separate loop below. All start flags are now parsed in a single pass.

Usage examples

# Set mobile viewport
rodney viewport 375 812 --mobile --scale 2

# Reset to browser default
rodney viewport --reset

# Start with viewport pre-configured
rodney start --viewport 375x812 --mobile --scale 2

# Screenshots now respect the active viewport
rodney viewport 375 812 --mobile --scale 2
rodney screenshot mobile.png    # Uses 375x812 viewport
rodney screenshot -w 1280       # Explicitly override to 1280

Test plan

• Unit tests for formatViewportDesc (basic, mobile, scale, combined, omission of scale 1/0)
• State serialization round-trip test (json.Marshal / Unmarshal)
• omitempty verification — zero-value viewport fields excluded from JSON
• End-to-end CDP test — EmulationSetDeviceMetricsOverride sets innerWidth and devicePixelRatio
• End-to-end CDP test — EmulationClearDeviceMetricsOverride restores defaults
• Reset clears persisted state fields
• Screenshot skips default viewport override when viewport is active
• go build passes
• All existing tests continue to pass

🤖 Generated with Claude Code

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.

[matthewbjones]

Related to older PR #33